Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $246.86   8.144%   $266.9643   $266.96   $266.95   $267.00  
  Purchase #2 $188.57   3.420%   $195.0191   $195.02   $195.00   $195.00  
  Purchase #3 $224.58   6.745%   $239.7279   $239.73   $239.75   $239.70  
  Purchase #4 $108.89   5.134%   $114.4804   $114.48   $114.50   $114.50  
  Purchase #5 $223.25   12.851%   $251.9399   $251.94   $251.95   $251.90  
  Purchase #6 $96.62   10.113%   $106.3912   $106.39   $106.40   $106.40  
  Purchase #7 $240.60   13.871%   $273.9736   $273.97   $273.95   $274.00  
  7 purchase totals = $1,329.37       $1,448.4964   $1,448.49   $1,448.50   $1,448.50